The present invention relates to an X-ray lithography apparatus which achieves a higher precision in precision manufacturing and a practical wafer-processing capability (a sufficient throughput).
The X-ray lithography apparatus has a higher resolution than known optical lithography apparatuses or the direct plotting technique using electronic beams and hence, is noted as the precision processing technology for superhigh-integrated submicron apparatuses. It is expected that X-ray lithography apparatus will soon replace optical lithography in the industry as it can obviate the difficulties encountered in the electronic beam lithography, e.g. low economic efficiency or low throughput and high cost in apparatus manufacture.
The X-ray lithography apparatus of which application has so far been limited to laboratories are mainly of the projection type apparatuses with dot-type X-ray source which is generally obtained by emanating and focusing electron beams on narrow spots on a fixed or rotary target. The irradiated X-ray beams in this type of apparatuses become extremely deviated from the parallel arrangement to therefore induce distortion in transferred patterns especially on the periphery of a wafer placed below the X-ray source. More particularly as shown in FIG. 1, a mask substrate 1 used in this type of technology comprises Si.sub.3 N.sub.4 thin film of ca.3 .mu.m thickness in order to fully tranmit soft X-ray which is easily absorbed. An interval S of 5-25 .mu.m is provided between the mask substrate 1 and a wafer 2 via a spacer 4 in order to prevent damages which might be caused by the contact with a resist surface 3 coated on the surface of the wafer 2. Due to this interval S, a distortion .DELTA. or the transfer error is caused in the patterns produced with the X-ray irradiated from a dot-like source 5, which distortion becomes conspicuous on the periphery of the wafer 2. This creates a critical defect in the manufacture of precision apparatuses where highly precise alignment is required. The adverse effect caused by the distortion on the periphery becomes serious when the wafer 2 is repeatedly processed to transfer different patterns.